linux-kernel - [PATCH v2] hexdump: fix for non-aligned buffers

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Date:	Mon, 22 Jun 2015 01:42:34 +0200
From:	=?UTF-8?q?Horacio=20Mijail=20Ant=C3=B3n=20Quiles?= <hmijail@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	David Howells <dhowells@...hat.com>,
	Vivek Goyal <vgoyal@...hat.com>, linux-kernel@...r.kernel.org,
	trivial@...nel.org, Joe Perches <joe@...ches.com>
Subject: [PATCH v2] hexdump: fix for non-aligned buffers

An hexdump with a buf not aligned to the groupsize causes
non-naturally-aligned memory accesses. This was causing a kernel panic on
the processor BlackFin BF527, when such an unaligned buffer was fed by the
function ubifs_scanned_corruption in fs/ubifs/scan.c .

To fix this, if the buffer is not aligned to groupsize in a platform which
does not define CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS, then change the
groupsize to 1, so alignment is no longer a problem.
This behavior is coherent with the way the function currently deals with
inappropriate parameter combinations, which is to fall back to safe
"defaults", even if that means changing the output format and the implicit
access patterns that could have been expected.

Signed-off-by: Horacio Mijail Antón Quiles <hmijail@...il.com>
---
Changes in v2:
  - Followed Joe Perches' indication to use IS_ALIGNED() for readability
  - Made the explanation, commit and code comments clearer (aligned vs 
        naturally aligned)

 lib/hexdump.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/lib/hexdump.c b/lib/hexdump.c
index 7ea0969..fef4ee1 100644
--- a/lib/hexdump.c
+++ b/lib/hexdump.c
@@ -123,6 +123,11 @@ int hex_dump_to_buffer(const void *buf, size_t len, int rowsize, int groupsize,
 		groupsize = 1;
 	if ((len % groupsize) != 0)	/* no mixed size output */
 		groupsize = 1;
+	
+	/* fall back to 1-byte groups if buf is not aligned to groupsize*/
+	if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) &&
+	    !IS_ALIGNED((uintptr_t)buf, groupsize))
+		groupsize = 1;

 	ngroups = len / groupsize;
 	ascii_column = rowsize * 2 + rowsize / groupsize + 1;
-- 
2.1.4

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